[misc] Move shared components to shared directory (#4286)

Moved the following directories:

```
  - management/client → shared/management/client
  - management/domain → shared/management/domain
  - management/proto → shared/management/proto
  - signal/client → shared/signal/client
  - signal/proto → shared/signal/proto
  - relay/client → shared/relay/client
  - relay/auth → shared/relay/auth
```

and adjusted import paths

shared/relay/client/dialer/quic/conn.go

@@ -0,0 +1,97 @@
+package quic
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/quic-go/quic-go"
+	log "github.com/sirupsen/logrus"
+
+	netErr "github.com/netbirdio/netbird/shared/relay/client/dialer/net"
+)
+
+const (
+	Network = "quic"
+)
+
+type Addr struct {
+	addr string
+}
+
+func (a Addr) Network() string {
+	return Network
+}
+
+func (a Addr) String() string {
+	return a.addr
+}
+
+type Conn struct {
+	session quic.Connection
+	ctx     context.Context
+}
+
+func NewConn(session quic.Connection) net.Conn {
+	return &Conn{
+		session: session,
+		ctx:     context.Background(),
+	}
+}
+
+func (c *Conn) Read(b []byte) (n int, err error) {
+	dgram, err := c.session.ReceiveDatagram(c.ctx)
+	if err != nil {
+		return 0, c.remoteCloseErrHandling(err)
+	}
+
+	n = copy(b, dgram)
+	return n, nil
+}
+
+func (c *Conn) Write(b []byte) (int, error) {
+	err := c.session.SendDatagram(b)
+	if err != nil {
+		err = c.remoteCloseErrHandling(err)
+		log.Errorf("failed to write to QUIC stream: %v", err)
+		return 0, err
+	}
+	return len(b), nil
+}
+
+func (c *Conn) RemoteAddr() net.Addr {
+	return c.session.RemoteAddr()
+}
+
+func (c *Conn) LocalAddr() net.Addr {
+	if c.session != nil {
+		return c.session.LocalAddr()
+	}
+	return Addr{addr: "unknown"}
+}
+
+func (c *Conn) SetReadDeadline(t time.Time) error {
+	return fmt.Errorf("SetReadDeadline is not implemented")
+}
+
+func (c *Conn) SetWriteDeadline(t time.Time) error {
+	return fmt.Errorf("SetWriteDeadline is not implemented")
+}
+
+func (c *Conn) SetDeadline(t time.Time) error {
+	return nil
+}
+
+func (c *Conn) Close() error {
+	return c.session.CloseWithError(0, "normal closure")
+}
+
+func (c *Conn) remoteCloseErrHandling(err error) error {
+	var appErr *quic.ApplicationError
+	if errors.As(err, &appErr) && appErr.ErrorCode == 0x0 {
+		return netErr.ErrClosedByServer
+	}
+	return err
+}